This seems sort of interesting as a sort of emergency backup, but it seems like the real solution for any sort of long distance/long duration in space is just making mass to orbit dramatically cheaper and shielding the spacecraft.
<https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation>
Even without earth-to-orbit costs, that mass has real costs, and reduces available payload.
If that shielding mass can be dual-use (e.g., water), reactive (e.g., electromagnets), or reduced to a very small amount (emergency shelters, wearable garments), it becomes more practicable. That still doesn't make it easy.
There's also a discontinuity in radiation exposure. Passing through radiation belts (e.g., Earth's van Allen belts, or those around Jupiter), and solar storms, are both predictable and special precautions can be taken. Cosmic ray radiation is unpredictable, high-energy, and is far harder to guard against. Some risk is inevitable.
In KSR's Mars Trilogy, they had an emergency shelter, seems reasonable if the bulk of the radiation exposure is predictable. But I'd personally feel better being shielded the entire time, given cosmic radiation.
Though yes, that does make the option of providing a radiation-hardened shelter available with less concern as to total mass.
IIR, the big problem is that the cosmic ray background radiation is far too predictable - there is a concerning amount of it 24x7x365. So your baseline choices are gritting your teeth and bearing it, or spending most of your time in a seriously hard shelter.
But yes, generally, it's at the very least a constant background flux (with occasional peaks), and all of it high-energy enough to make lightweight shielding of limited use.
Some types of radiation can be deflected by strong magnetic fields - based on the technology and power source of your craft, this might end up lighter than pure mass based shielding.
Or you can just have your crewed ships go as fast as possible, reducing exposure & avoiding some radiation sources all together - zipping through radiation belts & doing fast transits in the quiet part of the solar cycle.
How many orders of magnitude were you figuring for your "dramatically cheaper"?
Now, do not get me wrong: I got frickin' goose bumps when I saw the first Falcon touchdown. Goose bumps again when they did the first landing out in the open ocean. Of course I still love you! The pincers catching a starship booster were super awesome. Did I mention goose bumps? I am getting them as I write this, thinking back to those moments and now I want to re-watch all of those on youtube after I finish typing this.
But believing a single timeline prediction by Musk? No, forget it.
EDIT: haha, and yeah I did go re-watch and this is so super awesome when I got reminded of it: https://www.youtube.com/watch?v=bvim4rsNHkQ&t=1s No this is not meant as a jab btw. I love that they have this up. This is what many of us do in software development. Just we don't blow up actual frickin' spaceships to do it "It's just a rapid unscheduled disassembly!" ;)
"Technologically we can do self-driving, we'll just be killing any person that happens to stand in our way" does not qualify even as "technologically" for me ;)
The technology has to take into consideration the safety part. Legal, sure I'll give leeway. If you've seen some of the stuff Teslas have done past that predicted timeline, then no, they really did not qualify.
(https://arstechnica.com/space/2026/06/a-falcon-9-booster-tur...)
[0] https://en.wikipedia.org/wiki/In_situ_resource_utilization